The present invention relates to a hot air process heater for applying heat shrinkable tubing to a wire lead, and particularly to a slotted wall duct type heater for use with a conveyor which transports leads laterally.
U.S. Pat. No. 3,812,568 discloses a hot air duct type heater having air supply plenums on either side of a passage through which a terminated lead having a section of shrink tubing positioned thereon is transported laterally. The plenums each have a plurality of apertures which admit air to the passage to shrink the section onto the lead. The entire tubing section is exposed to heat and thus must be positioned on the terminal with no more overlap than necessary to compensate for longitudinal shrinking, or else the section of tubing would shrink over the end of the terminal which could preclude mating with another terminal.
Other heaters used for shrinking shrink tubing utilize lamps or other radiant elements, which provide uniform heat but offer the disadvantage of overheating the product if it is not moved through quickly. Further, if a section of tubing becomes lodged on a radiant element, it could be damaged or result in combustion.
It would be desirable to provide a heating apparatus which had the capability to heat the shrink tubing over only part of its length as positioned on the terminated end of a wire lead. This would permit placing a section of tubing on the terminal with more overlap than necessary to compensate for longitudinal shrinkage without shrinking the additional overlap onto the end of the terminal. Thus a terminated lead could be insulated with shrink tubing having sufficient overlap to preclude short circuiting a live lead, but still readily permit termination. In addition to the safety factor provided by having tubing extend beyond the terminal, if the tubing is not shrunk around the mating portion of a spring action terminal the resiliency is not altered and the terminal may be mated more easily.